The present invention relates to an integrated electronic device and a fabrication method thereof, more particularly to the integrated electronic device having an electric connection for connecting a semiconductor chip with a circuit board and fabrication method thereof.
For higher integration of semiconductor chips on a circuit board, a flip-chip method has been developed which enables bare semiconductor chips to be mounted directly on a circuit board by connecting each of electrodes between the semiconductor chips and the circuit board using soldering metal. However, a drawback on a soldering metal connection is a fact that a surface of an aluminium interconnection layer, widely used in LSI circuit, has repellency against melt of soldering metal, which is often called a wettability problem. It could be avoided by coating the aluminium surface by a metal having an adhesive tendency to soldering metal, but it eventually makes the fabricating steps more complex. Another unfavorable effect of a soldering metal connection is that as shown in FIG. 7, a rigid connection between electrodes 32, 34 by soldering metal 33 often results in a crack 36 due to a repetitive local stress concentration caused by discrepancy in thermal expansion coefficient between a semiconductor chip and a circuit board. To avoid these foregoing problems, as shown in FIG. 8A, a bump 55 containing dispersed liquid metal particles 53 of indium-gallium in flux vehicle 54 for a liquid connection on a gold electrode 52 has been proposed, however, surface tension of the liquid metal 53 against gold surface is still so high that the liquid metal often makes itself droplets 53 on the gold electrode 52 after heating process as shown in FIG. 8B.
It is an object of the present invention to provide a method for fabricating an integrated electronic device having a soldering metal connection between a semiconductor chip and a circuit board free from the wettability problem on the soldering metal connection to an electrode of the semiconductor chip.
It is another object of the present invention to provide a method for fabricating an integrated electronic device having a soldering metal connection between a semiconductor chip and a circuit board free from disconnection failures caused by thermal stress.
It is a further object of the present invention to provide an integrated electronic device having a soldering metal connection between a semiconductor chip and a circuit board free from the wettability problem on the soldering metal connection to an electrode of the semiconductor chip.
It is a still further object of the present invention to provide an integrated electronic device having a soldering metal connection between a semiconductor chip and a circuit board free from disconnection failures caused by thermal stress.
One aspect of the present invention is a method for fabricating an integrated electronic device having an electric connection between a first electrode of a semiconductor chip and a second electrode of a circuit board comprising the steps of:
forming a first bump made of a first metal component on the first electrode, a surface of the first electrode having repellency against melt of the first metal component;
forming a second bump made of a second metal component on the second electrode opposite to the first bump in a position; and
forming a connection part made of an eutectic alloy consisting of the first metal component and the second metal component between the first bump and the second bump so as to make an electric connection between the first electrode and the second electrode.
Another aspect of the present invention is a method for fabricating an integrated electronic device having an electric connection connecting a first electrode of a first substrate with a second electrode of a second substrate, both surfaces of the first and second electrodes having an adhesive tendency to molten metal, the method comprising the steps of:
forming a metal bump on the surface of the first electrode, the metal bump being made of a soldering metal alloy consisting of a solid phase component and a liquid phase component at an operating temperature; and
forming an electric connection between the first electrode and the second electrode by heating the soldering metal alloy so as to adhere to the surface of the second electrode.
Still another aspect of the present invention is a method for fabricating an integrated electronic device having an electric connection between a first electrode of a first substrate and a second electrode of a second substrate comprising the steps of:
forming a first metal layer on a surface of a first electrode on a first substrate, the first metal layer capable of composing an eutectic alloy with gallium (Ga);
forming a bump of Ga-rosin mixture on the first metal layer selectively; and
forming the electric connection between the first electrode and the second electrode by heating the bump of Ga-rosin mixture maintaining the bump of the Ga-rosin mixture in contact with the second electrode to react gallium in the Ga-rosin mixture with the first metal layer into the alloy capable to adhere to the first and second electrodes.
The technique according to the present invention can be applied to an electro-mechanical device such as a saw-tooth device or an optoelectronic device as well as a multi-chip semiconductor module having a multi-layered circuit board.